Urinary extravasation in the fetus with obstructive uropathy.

Urinary extravasation resulting in either urinary ascites or an isolated perirenal urinoma is relatively common in the fetus with severe obstructive uropathy. We examined the effect of fetal urinary extravasation on the developing kidney and abdominal wall in 12 fetuses taken from a series of 44 cases of fetal urinary tract obstruction. Based on this experience, we conclude that fetal urinary extravasation has predictable pathophysiologic consequences. Fetal urinary ascites appears to ameliorate obstruction-induced renal dysplasia by decompressing the high-pressure, obstructed fetal urinary system. Conversely, contained urinomas secondary to ureteropelvic junction obstruction provide inadequate decompression and are associated with renal dysplasia. Last, the severity of abdominal wall laxity (prune belly) relates directly to the timing and degree of fetal ascites.